generation, instead of election,--and reducing the question to
mathematical simplicity of statement: species are lines of individuals
coming down from the past and running on to the future,--lines
receding, therefore, from our view in either direction. Within our
limited view they appear to be parallel lines, as a general thing
neither approaching to nor diverging from each other. The first
hypothesis assumes that they were parallel from the unknown beginning
and will be to the unknown end. The second hypothesis assumes that the
apparent parallelism is not real and complete, at least aboriginally,
but approximate or temporary; that we should find the lines convergent
in the past, if we could trace them far enough; that some of them, if
produced back, would fall into certain fragments of lines, which have
left traces in the past, lying not exactly in the same direction, and
these farther back into others to which they are equally unparallel.
It will also claim that the present lines, whether on the whole really
or only approximately parallel, sometimes fork or send off branches on
one side or the other, producing new lines, (varieties,) which run for
a while, and for aught we know indefinitely, when not interfered with,
near and approximately parallel to the parent line. This claim it can
establish; and it may also show that these close subsidiary lines may
branch or vary again, and that those branches or varieties which are
best adapted to the existing conditions may be continued, while others
stop or die out. And so we may have the basis of a real _theory_ of
the _diversification_ of species; and here, indeed, there is a real,
though a narrow, established ground to build upon. But, as systems of
organic Nature, both are equally _hypotheses_, are suppositions of
what there is no proof of from experience, assumed in order to account
for the observed phenomena, and supported by such indirect evidence as
can be had. Even when the upholders of the former and more popular
system mix up revelation with scientific discussion,--which we decline